Induction foil cap sealers are well known. Referring to FIG. 1, a prior art induction foil cap sealer includes induction head 10 which includes a plurality of field coils 12. In operation, field coils 12 receive an electrical current which causes the development of magnetic fields that project away from field coils 12. The projected magnetic fields are schematically shown as circular lines surrounding field coils 12 for illustration purposes only. The magnetic fields projecting from field coils 12 are used for sealing a cap onto an opening of a bottle in the following manner.
Cap 14 is mechanically coupled to the opening of bottle 16 and placed under induction head 10. Due to the mechanical coupling between cap 14 and bottle 16, metallic foil 18, which is received in cap 14, is pressed between the end of cap 14 and the sealing edge of the opening of bottle 16. Included inside cap 14 is polymer sealing film 17 which is interposed between metallic foil 18 and the opening of bottle 16. Optionally, wax layer 20 and pulp board liner 22 are also included in cap 14 and sandwiched between metallic foil 18 and the closed end of cap 14.
To effect the seal, magnetic fields that project from field coils 12 permeate cap 14 and cause foil 18 to heat up. The heat so generated causes polymer sealing film 17 to melt and thus seal metallic foil 18 to the opening of bottle 16. As a result, a hermetic seal between metallic foil 18 and bottle 16 is obtained which can survive the removal of cap 14. If optional wax layer 20 is used, the generated heat melts wax layer 20 further enhancing the hermetic effect.
Induction head 10 may assume any number of shapes depending on the type of cap used. FIGS. 2A-2C illustrate three examples of induction heads.
Assuring the quality of the hermetic seal is commercially important. For example, when the content of a container is medicine, it is important for the consumer to know that the container has been sealed since leaving the manufacturer's plant. Otherwise, a consumer may suspect tampering and return the product, which results in the increase in the overall cost to the manufacturer. In addition, a hermetic seal may be required to keep the content of a container unexposed to environmental factors such as moisture in order to avoid damage to the content. In either case, assessing the quality of the seal before the container leaves the manufacturer is of great interest.
Several factors affect the quality of the seal. One factor is the amount of time a container is exposed to induction heating. If the amount of time is too short, a good seal may not be obtained. If the amount of time is too long, there may be overheating, which can damage the container, the seal, the product, and the sealing head itself.
The amount of exposure time is directly related to how fast a container passes under induction head 10. Thus, the speed of the carrying platform which carries the container, e.g. a conveyor belt, is important in attaining a good induction seal.
It would be desirable to have an induction sealing system and an induction sealing method that can monitor the amount of induction exposure in order to produce a good seal quality.